# bootable ext. USB SSD for backup

Matthew Seaman matthew at FreeBSD.org
Fri Mar 17 15:22:44 UTC 2017

```On 2017/03/16 20:29, Valeri Galtsev wrote:
> On Thu, March 16, 2017 3:13 pm, Ralf Mardorf via freebsd-questions wrote:
>> On Thu, 16 Mar 2017 14:56:07 -0500 (CDT), Valeri Galtsev wrote:
>>> Junior programmer faithfully thinks that one kilobyte is exactly 1000
>>> bytes.
>>>
>>> Senior programmer faithfully thinks that one kilogram is exactly 1024
>>> grams.

>> When I programmed Commodore 64 Assembler a KB was 1024 B, nowadays I
>> call it a KiB, to distinguish between 2^10 and 10^3, see
>> https://en.wikipedia.org/wiki/Kibibyte .
>>
>> I dislike this joke, since senior programmers usually are also senior
>> electronics technicians,

> Right, I've heard the joke in a different language, so I had to make up
> some equivalent for "computer geek" and otherwise person. Sysadmin doesn't
> fit there too as,e.g. myself, I have two degrees: electical engineering
> and computer science, so megaohms, and kilovolts are kind of there. So, I
> don't know what to call the person so torn off the real life (as I heard
> the joke in metric based country, where "kilo-" is used everywhere).

I, for one, welcome our new SI / NIST overlords.

But then I started out as a scientist, and the fact the the SI prefixes
(p n µ m 1 k M G P etc.) always indicate powers of 10^3 is engraved on
my soul.

For anyone unclear as to why this is a good idea, consider the
statement: "we peaked at 1.1Gb/s transfer rate."  That's computery stuff
right?  So it really means 1181116006.4b/s doesn't it?

Nope.  Bandwidth has always been measured in strict SI units -- mostly
because it was physicists, electrical engineers and radio technicians
got there first, and there's the Fourier relation between 'bits
(samples) per second' and 'maximum signal frequency' that makes no sense
at all if you start throwing powers of 2^10 around.  (Google for
'Nyquist sampling theorem' if you're interested).

Now work out how long it's going to take to transmit 10GB of data
enough (remember that 1B (byte) = 8b (bits) though.) Or did I mean 10GiB
of data?

It's this sort of confusion that leads to embarrassing mistakes like
your Mars orbiter enjoying some unscheduled lithobraking[*].

And, for an encore, if anyone could bring me the head of what ever
bright spark in Electricity generation thought that the bastard mongrel
of a unit 'kWh' was a good idea, I'd be forever in your debt.  It's a
daft unit, when there is a perfectly acceptable and rigorous SI
alternative which is even right around the same order of magnitude: the
MegaJoule. 1 kWh is 3.6 MJ.

Cheers,

Matthew

[*] OK, that was down to American Imperial vs SI units, but that is
exactly the same sort of stupidity.

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